Nothing terribly useful out there - there used to be some debuff helper plugin, but I never got them working and I don't think its actively maintained.

Considering that one of the roles for an LM is debuffing and crowd control, the main thing is to make sure the debuffs and cc's are active 100% of the time. But this really just comes down to watching the cooldown's and popping a skill the moment it becomes available again. Perhaps a plugin might make this a bit easier, but I find grouping the skills together on the quickbar(s) is sufficient.

Stun-immunity is another matter - even with the 'only show effects cast by you' enabled, it takes a bit of practise to get the timing right to keep it up on a full raid. A plugin might help here... but I don't know of any that are suitable.

CCTimer tracks CC effects. It also tracks the current CC state on your target, and when properly calibrated has a bunch of indicators for handling CC timing on targets. (I.e., you can't root a rooted target, so there's an indicator that'll tell you if there is less than this amount of time remaining on a CC effect, and the CC effect is a root, you can cast cracked earth on the target, and it'll actually get rooted.) On the other hand, the thing is stupidly complicated, and I have to reread the documentation each time if I don't use it for a month or so. And I wrote the thing.

PartyFrame is a pretty standard fellowship/raid vitals replacement. By default, it's setup to track class specific buffs on people in your fellowship/raid.